IT STARTS WITH PHYTOPLANKTON
In open ocean environments, microscopic
phytoplankton are the main source of productivity.
Like plants on land, phytoplankton use energy from
the sun, nutrients and water to convert carbon dioxide
(CO 2 ) into oxygen (O 2 ). Through this process, known
as photosynthesis, phytoplankton store energy from
the sun to power the entire ocean ecosystem, as
zooplankton eat the phytoplankton and larger animals
eat the zooplankton. As the larger animals die and
sink to the bottom, they in turn become the energy
source for the ecosystem on the ocean floor.
Areas where large amounts of phytoplankton are
produced and attract other animals from higher upworld standards there are very few major river systems
to bring nutrients into its marine environment. This is
especially the case off southern Australia. Similarly,
compared to many parts of the world, direct rainfall
into the oceans surrounding Australia is relatively low.
Most of the productivity in Australian waters is based
off eddies (whirlpools that mix cooler and warmer
water), forming in either the Eastern Australian
Current (EAC) or the Llewelyn Current as they
flow south. Some canyon systems also form more
predictable upwellings, where nutrient-rich deep
water is driven towards the surface. For example, this
occurs at the Bonney upwelling in the eastern Great
Australian Bight and western Bass Strait. Underwater
seamounts such as those off eastern Australia can also
be hotspots for productivity when currents hit their
slopes and redirects deep nutrient-rich waters up to
the surface.
OCEAN PRODUCTIVITY
Highly productive waters need good light, lots of
nutrients and high oxygen levels for fish to thrive.
Warm tropical and sub-tropical waters tend to be
nutrient poor and have relatively low oxygen levels.
High productivity areas tend to occur where nutrient-
rich deep-water upwellings occur or warm and cold
ocean currents mix with surface waters. Typically,
these conditions occur along both coasts of South
America, around Alaska, New England, the North Sea
and the west coast of Africa. In most cases, upwellings
or cold-water currents bringing nutrient-rich waters
into sub-tropical regions is directly linked to high
productivity levels.
“Underwater
seamounts
such as those
off eastern
Australia
can be
hotspots for
productivity.”
Australia is the only
continent with warm
currents pushing
southward on both
its eastern and
western coasts. With
few nutrients flowing
in from the land, and
a generally narrow
continental shelf, the
nation’s waters yield
low productivity.
Upwellings caused by
the swirling current
eddies draw seafloor
nutrients up to the
surface to feed much
of the phytoplankton
growth that initiates
the offshore food
chain.Australia produces
high-quality seafood,
but despite its
vast coastline,
the nation’s ocean
productivity is a
fraction of that
produced by the
more fertile waters
surrounding North
America and other
continents.bluewatermag.com.au 69